Kinematic evaluation of the back in the sport horse with back pain

REASONS FOR PERFORMING STUDY: Earlier studies have developed a clinical tool to evaluate objectively the function of the equine back. The ability to differentiate horses with back pain from asymptomatic, fully functioning horses using kinematic measures from this tool has not been evaluated. OBJECTIVES: To compare the kinematics of the back at walk and trot in riding horses with back dysfunction to the same parameters in asymptomatic sport horses. METHODS: The kinematics of the back in 12 horses with impaired performance and back pain were studied at walk and trot on a treadmill. Data were captured for 10 sees at 240 Hz. Range of movement (ROM) and intravertebral pattern symmetry of movement for flexion and extension (FE), lateral bending (LB) and axial rotation (AR) were derived from angular motion pattern data and the results compared to an earlier established database on asymptomatic riding horses. RESULTS: At walk, horses with back dysfunction had a ROM smaller for dorsoventral FE in the caudal thoracic region (T13 = 7.50 degrees, T17 = 7.71 degrees; P<0.05), greater for LB at T13 (8.13 degrees; P<0.001) and smaller for AR of the pelvis (10.97 degrees; P<0.05) compared to asymptomatic horses (FE-T13 = 8.28 degrees, FE-T17 = 8.49 degrees, LB-T13 = 6.34 degrees, AR-pelvis = 12.77 degrees). At trot, dysfunctional horses had a smaller (P<0.05) ROM for FE at the thoracic lumbar junction (T17 = 2.46 degrees, L1 = 2.60 degrees) compared to asymptomatic horses (FE-T17 = 3.07 degrees, FE-L1 = 3.12 degrees). CONCLUSIONS: The objective measurement technique can detect differences between back kinematics in riding horses with signs of back dysfunction and asymptomatic horses. The clinical manifestation of back pain results in diminished flexion/extension movement at or near the thoracic lumbar junction. However, before applying the method more extensively in practice it is necessary to evaluate it further, including measurements of patients whose diagnoses can be confirmed and long-term follow-ups of back patients after treatment. POTENTIAL RELEVANCE: Since the objective measurement technique can detect small movement differences in back kinematics, it should help to clinically describe and, importantly, objectively detect horses with back pain and dysfunction.     

A preliminary report on estimating the pressures exerted by a crank noseband in the horse

The pressures applied to horses via restrictive nosebands are of growing concern to equitation scientists and horse sport administrators. They prevent the expression of normal behavior, may compromise blood flow, and even damage bone. This report describes an approach to estimate in vivo pressures applied to the dorsal and ventral aspects of a horse's nose via a so-called crank noseband. A load cell calibrated over a load range of 0-100 N was integrated into a commercially available crank noseband. These force values were combined with anatomical curvature data to estimate the pressure applied by the noseband to the underlying tissue at any point along the internal surface of the noseband using Laplace's law. Partial profiles of both dorsal and ventral aspects of the horse's nose, at a position corresponding to that of the noseband, were taken by contouring a flexible curve ruler to the nose. The ruler was stiff enough to retain the profile when removed from the nose, thereby allowing faithful transfer of the profile to paper for digitization. Once digitized, straightforward mathematical algorithms were used to provide an analytical expression describing each profile, to calculate profile curvature point by point, and, using measured noseband force values, to transform the curvature into a corresponding sub-noseband pressure profile. This process was used to study pressures applied when the horse chewed hay, chewed concentrate mix, and when it was cued to step backward. The calculated pressures ranged from 200 to 400 mm Hg; pressures that, in humans, are associated with nerve damage and other complications. As such, these preliminary data strongly suggest the need for more research in this domain. The current approach should inform some of the welfare concerns in ridden horses but should also be of use in studies of oral behaviors around foraging as well as crib biting and wind sucking.     

Usability of normal force distribution measurements to evaluate asymmetrical loading of the back of the horse and different rider positions on a standing horse

Pressure measurement devices in equine sports have primarily focused on tack (saddle pads and saddle fitting methods). However, saddle pressure devices may also be useful in evaluating the interaction and distribution of normal forces between the horse and rider, including rider position and riding technique. This study examined the validity, reliability, repeatability and possibilities of using a saddle pressure device to evaluate rider position. All measurements were performed using a standing horse. Validity was tested by calculating the correlation coefficient between measured normal force and the weight of the rider. Repeatability was tested by calculating intra-class correlation coefficients. The use of normal force measurements to evaluate horse–rider interaction was tested by adding a known weight to saddle or rider and collecting measurements with the rider sitting in four different positions.The device was found to be valid and reliable for force measurements when the measurement device was not replaced. The system could be used to determine the expected differences with added weight and in different rider positions. The normal force distribution measurement device proved to be a valid and reliable tool for studying the interaction between a rider and a static horse provided it is positioned carefully and consistently relative to both the horse and the saddle.     

Long-term follow-up of manipulative treatment in a horse with back problems

In order to objectively quantify the effect of manipulation on back-related locomotion anomalies in the horse, a recently developed kinematic measuring technique for the objective quantification of thoracolumbar motion in the horse was applied in a dressage horse that was suffering from a back problem. In this horse, clinically, a right-convex bending (scoliosis) from the 10th thoracic vertebra to the second lumbar vertebra was diagnosed. As a result, there was a marked asymmetric movement of the thoracolumbar spine. Functionally, there was severe loss of performance. Thoracolumbar motion was measured in terms of ventrodorsal flexion, lateral flexion, and axial rotation using an automated gait analysis system. Measurements were repeated before and 2 days after treatment, before the second treatment 3 weeks later, and at 4 weeks and 8 months after the second treatment to assess long-term effect. At the same time, performance of the horse was assessed subjectively by the trainer as well. Symmetry of movement improved dramatically after the first treatment. After this, there was a slight decrease in symmetry, but 8 months after the last treatment the symmetry indexes for the various joints were still considerably better than during the first (pre-treatment) measuring session. Subjectively, the trainer did not notice improvement until after measurement session 4. Between sessions 4 and 5 (at 4 weeks and 8 months after the second treatment) there was a change of trainer. The new trainer did not report any back problem, and succeeded in bringing the horse back to its former level in competition. It is concluded that manipulation had a measurable influence on the kinematics of the thoracolumbar spine. However, it is recognized that an improvement in symmetry of motion is not equivalent to clinical improvement and that other measures, such as changes in management, may be more decisive.     

Echocardiographic and right-sidedcardiac pressure comparison of the mule and horse

There are few physiologic studies that substantiate thepopular belief that mules are superior to horses as working animals. The purpose of this study was to compare selected cardiac dimensions and right-sided cardiac pressures of mules and horses. Using 2-D real time and M-mode echocardiography and transjugular cardiac catheterization resting cardiac dimensions and right-sided pressures were recorded from 10 adult mules and 10 adult horses. The mules and horses were similar in size and physical condition, and both groups had served equally as pack animals. The end diastolic left ventricular lumen diameter, interventricular septal thickness, left ventricular free wall thickness, and aortic root diameter measured (mean ± SD) 9.51 ±0.92 cm, 2.63±0.34 cm, 2.28±0.31 cm, 7.9±0.57 cm, respectively, in mules, and 9.83±0.87 cm, 2.83±0.29 cm, 2.39±0.33 cm, 7.9±0.36 cm, respectively, in horses. The end systolic left ventricular lumen diameter measured 5.79 cm in mules and 5.94±0.99 cm in horses, yielding left ventricular luminal shortening fractions of 39.2±7.15% in mules and 39.7±6.91% in horses. Right atrial mean pressure was 5.3±2.3 mm of Hg in mules and 5.8±1.2 mm Hg in horses. Right ventricular peak systolic pressure was 47.9±4.9 mm Hg in mules and 47.7±3.5 mm Hg in horses. Pulmonary artery mean pressure was 27.3±3.2 mm Hg in mules and 28.1±3.6 mm Hg in horses. No significant differences were detected between mules and horses for the resting cardiac dimensions examined or right-sided pressures measured.     

Radiologic examination of the spine in "back problems" of the standing horse]

The radiological examination of the thoracolumbar spine of a horse with a potential back problem is most important in order to come to a diagnosis and the imaging method of choice. The use of parallel grid-cassettes, appropriate films, rare earth screens and aluminium filters requires radiographic equipment with an output of 60-120 kV and 25-90 mAs. By use of this technique in the standing horse it is possible to obtain radiographs of the summits of the dorsal spinal processes of the thoracolumbar spine from the first thoracic (T1) to approximately the third of fourth lumbar vertebrae (L3/4). Since the thickness of soft tissue is increasing from distal to proximal it is necessary to increase the output to image the processus articulares craniales et caudales. Therefore additional radiographs have to be taken.     

Development of an intrauterine distension pressure for hysteroscopy in the horse

Diagnostic and operative hysteroscopy have offered an advance in equine fertility diagnostic and equine fertility surgery. A distension of the uterine cavity and an establishment of a continuous intrauterine pressure are basic requirements for complete visualisation of intrauterine structures and safe and efficient surgical procedures. Superelevated pressure and resorption of distension media may result in fatal complications. Intrauterine pressure was monitored in 28 healthy di- or anestrus mares during hysteroscopy via a transcervically inserted catheter. Mares were sedated with xylazine and levornethadon and fixed in a stock. The pressure which was elementary for complete visualisation Parb, the pressure with onset of transcervical efflux of distension medium Pcerv and the maximum intrauterine pressure Pmax that could be obtained were determined. Complete visualisation of intrauterine structures could be achieved with a mean pressure of 17.8 +/- 5.5 mm Hg (mean +/- s) and a range of 12.8 to 28.6 mm Hg. Spontaneous efflux of distension media was registered in mares following further insufflation at a significantly higher (p < 0.001) intracavitary pressure of 62.5 +/- 10.0 mm Hg (mean +/- s). Maximum pressure Pmax that could be obtained was found to be significantly higher (p < 0.001) than Parb but also significantly higher than Pcerv with 101.6 +/- 24.4 mm Hg (mean +/- s). Clinical or cardiological signs of discomfort or affection on the circulatory system were only registered while Pmax was applicated. The results indicate, that a safe and efficient hysteroscopy can be performed with a mean pressure of 17.8 mm Hg and an upper pressure limit of 30 mm Hg.     

Relationship between the forces acting on the horse's back and the movements of rider and horse while walking on a treadmill

Reasons for performing study: The exact relationship between the saddle pressure pattern during one stride cycle and the movements of horse and rider at the walk are poorly understood and have never been investigated in detail. Hypothesis: The movements of rider and horse account for the force distribution pattern under the saddle. Method: Vertical ground reaction forces (GRF), kinematics of horse and rider as well as saddle forces (FS) were measured synchronously in 7 high level dressage horses while being ridden on an instrumented treadmill at walk. Discrete values of the total saddle forces (FStot) were determined for each stride and related to kinematics and GRF. The pressure sensitive mat was divided into halves and sixths to assess the force distribution over the horse's back in more detail. Differences were tested using a one sample t test (P<0.05). Results: FStot of all the horses showed 3 peaks (P1‐P3) and 3 minima (M1‐M3) in each half‐cycle, which were systematically related to the footfall sequence of the walk. Looking at the halves of the mat, force curves were 50% phase‐shifted. The analysis of the FS of the 6 sections showed a clear association to the rider's and horse's movements. Conclusion: The saddle force distribution during an entire stride cycle has a distinct pattern although the force fluctuations of the FStot are small. The forces in the front thirds were clearly related to the movement of the front limbs, those in the mid part to the lateral flexion of the horse's spine and the loading of the hind part was mainly influenced by the axial rotation and lateral bending of the back. Potential relevance: These data can be used as a reference for comparing different types of saddle fit.     

Effects of intravenous lidocaine overdose on cardiac electrical activity and blood pressure in the horse

This study aimed to identify blood serum lidocaine concentrations in the horse which resulted in clinical signs of intoxication, and to document the effects of toxic levels on the cardiovascular and cardiopulmonary systems. Nineteen clinically normal mature horses of mixed breed, age and sex were observed. Lidocaine administration was initiated in each subject with an i.v. loading dose of 1.5 mg/kg bwt and followed by continuous infusion of 0.3 mg/kg bwt/min until clinical signs of intoxication were observed. Intoxication was defined as the development of skeletal muscle tremors. Prior to administration of lidocaine, blood samples for lidocaine analysis, heart rate, mean arterial blood pressure, systolic blood pressure, diastolic blood pressure, respiratory rate and electrocardiographic (ECG) data were collected. After recording baseline data, repeat data were collected at 5 min intervals until signs of intoxication were observed. The range of serum lidocaine concentrations at which the clinical signs of intoxication were observed was 1.85-4.53 microg/ml (mean +/- s.d. 3.24 +/- 0.74 microg/ml). Statistically significant changes in P wave duration, P-R interval, R-R interval and Q-T interval were observed in comparison to control values, as a result of lidocaine administration. These changes in ECG values did not fall outside published normal values and were not clinically significant. Heart rate, blood pressures and respiratory rates were unchanged from control values. This study establishes toxic serum lidocaine levels in the horse, and demonstrates that there were no clinically significant cardiovascular effects with serum lidocaine concentrations less than those required to produce signs of toxicity.     

The effect of rising and sitting trot on back movements and head‐neck position of the horse

Reason for performing study: During trot, the rider can either rise from the saddle during every stride or remain seated. Rising trot is used frequently because it is widely assumed that it decreases the loading of the equine back. This has, however, not been demonstrated in an objective study. Objective: To determine the effects of rising and sitting trot on the movements of the horse. Hypothesis: Sitting trot has more extending effect on the horse's back than rising trot and also results in a higher head and neck position. Methods: Twelve horses and one rider were used. Kinematic data were captured at trot during over ground locomotion under 3 conditions: unloaded, rising trot and sitting trot. Back movements were calculated using a previously described method with a correction for trunk position. Head‐neck position was expressed as extension and flexion of C1, C3 and C6, and vertical displacement of C1 and the bit. Results: Sitting trot had an overall extending effect on the back of horses when compared to the unloaded situation. In rising trot: the maximal flexion of the back was similar to the unloaded situation, while the maximal extension was similar to sitting trot; lateral bending of the back was larger than during the unloaded situation and sitting trot; and the horses held their heads lower than in the other conditions. The angle of C6 was more flexed in rising than in sitting trot. Conclusions and clinical relevance: The back movement during rising trot showed characteristics of both sitting trot and the unloaded condition. As the same maximal extension of the back is reached during rising and sitting trot, there is no reason to believe that rising trot was less challenging for the back.     

Effect of cardiac arrhythmia on left ventricular and aortic blood pressure parameters in the horse

Transaortic blood pressures were recorded in seven horses using catheter mounted transducers during various types of supraventricular arrhythmia. Changes in left ventricular (LV) and aortic (Ao) pulse contours were associated with variation in pulse interval (PI). When PI lengthened there was a rise in LV end diastolic pressure (LVEDP) associated with a prolonged filling time. In contrast, a long PI resulted in a reduced end diastolic Ao pressure (AoEDP) due to a prolonged arterial 'run off'. LVdP/dt max representing the peak rate of rise of pressure during the isovolumic contraction period was not consistently affected by changes in PI. Stepwise linear regression was used to examine the simultaneous relationships of a number of variables derived from the LV and Ao contours. Peak LV pressure (LVPp) was directly related to AoEDP (seven of seven horses) and LVEDP (four of seven). Ao systolic pulse pressure (SPP) was directly related to LVEDP (four of seven) and inversely related to AoEDP (three of seven). Neither LVPp nor SPP were consistently related to LVdP/dt max. The peak positive gradient between LV and Ao pressures was inversely related to AoEDP (six of seven) and directly related to LVEDP and LVdP/dt max (three of seven). The peak rate of rise of the Ao pressure contour during ejection (AodP/dt max) was inversely related to AoEDP (seven of seven) and directly related to LVEDP (four of seven). It was also directly related to LVdP/dt max in four horses but was inversely related in one. The peak rate of fall of the LV pressure contour during relaxation (-LVdP/dt max) was directly related to LVPp (five of seven).     

Effect of topical atropine on intraocular pressure and pupil diameter in the normal horse eye

The objective was to determine whether topically administered 1% atropine would alter intraocular pressure. The animals studied were four healthy adult horses. Intraocular pressure and pupil diameter were measured prior to and during a 2-day period of treatment with 1% atropine sulfate. No significant changes in intraocular pressure occurred as a result of the treatment with atropine. Pupil diameter increased significantly after atropine was applied. Available information on the outflow of aqueous humor from the horse eye suggests that atropine might reduce intraocular pressure in the horse by increasing uveoscleral outflow. This could prove beneficial in the treatment of equine glaucoma. We could not confirm a significant pressure-lowering effect of atropine. It is possible, however, that a longer treatment period may be required or that atropine may have a more profound effect on glaucomatous globes.     

Symposium on back problems in the horse. (3) Diseases of the horse's spine-"comparative aspects".

The structural differences in the spine of the horse and man are compared. These, together with the different uses to which the spine is put, explain the different patterns of disease. Impingement of the spinous processes is discussed in detail including surgical treatment. Comments are also made on sacroiliac strain and manipulation of the spine.     

Intracompartmental muscle pressure, temperature and pH in the horse undergeneral anesthesia

Intracompartmental muscle pressure, temperature and pH were measured in a group of 23 anesthetized horses in an attempt to elucidate the etiology of post-anesthetic lameness (PAL). The intramuscular pressure remained reasonably constant throughout anesthesia in most horses, while muscle temperature and pH fell. Five of the horses became lame after anesthesia. Two of these lame horses exhibited atypical trends in the physiological variables measured. The etiology of PAL is discussed in the lightof the results.     

Indirect measurement of mean blood pressure in the normotensive and hypotensive horse.

Indirect mean arterial pressure was obtained from the tails of 78 anaesthetised and unanaesthetised normotensive and hypotensive horses. Data were obtained to determine the optimum cuff width in relation to tail circumference. A cuff that is too wide under-estimates and a cuff that is too narrow over-estimates blood pressure. With the optimum cuff width, which is slightly in excess of about one-fifth of the tail circumference, indirect mean blood pressure was obtained consistently in normotensive and hypotensive animals with mean blood pressures of 40 mmHg and frequently in animals with pressure as low as 30 mmHg.